3-D video-oculography sheds new light on pediatric strabismus

The role of luminance in generating common forms of pediatric strabismus and nystagmus is the current focus of study in the ocular motor physiology laboratory in the Department of Ophthalmology at Mayo Clinic in Rochester, Minn. The study uses video-oculography to noninvasively record eye movements in children with strabismus and nystagmus. Researchers will use the data to investigate the role of fixation versus luminance input to the two eyes in causing strabismus and nystagmus.

"Video-oculography can detect positional and velocity changes of the two eyes that cannot be detected on clinical examination. Quantitative analysis of these responses should provide new information about the neurophysiology of these disorders," says Michael C. Brodsky, M.D., who leads the research team. "It will also provide a means to evaluate and compare treatments."

Three-dimensional eye movement recordings are difficult to obtain in children because these recordings usually necessitate placement of thick contact lenses on the eyes during the test. This 3-D video-oculography system, however, measures horizontal, vertical and torsional eye movements using infrared light in a manner that is noninvasive and more applicable to children.

Noninvasive examinations

During the 10- to 15-minute examination, the patient is seated comfortably and merely looks straight ahead. The patient wears a lightweight (about 20 ounces) rubber mask, much like a scuba mask. The inside of the mask contains an infrared light source and two video cameras off to the side. The cameras measure the positions of the two eyes as the patient looks in different directions. The only risks to the patient include temporary feeling on the face and red marks from wearing the mask.

The 3-D video-oculography device records eye position at 250 hertz and is considered minimal risk for use in children and adults. Because the system works in the infrared wavelengths, it is capable of recording in either light or dark. The video camera records horizontal and vertical eye movements and also the torsional position (the degree of twisting) of the eyes in each position of gaze.

"This torsional measurement is critical to establishing which neural pathways are commanding the eyes to behave normally or abnormally during eye movement," says Dr. Brodsky. "It allows us to determine which muscles and nerve centers are affected within the brain, and could help direct surgical treatment with unprecedented precision. It will also provide measurement of the position and eye velocity of the eyes to determine whether a given surgery is effective for nystagmus.

"Some forms of pediatric strabismus, such as intermittent exotropia and dissociated vertical divergence, are modulated by luminance input," says Dr. Brodsky. "Similarly, infantile nystagmus and latent nystagmus are influenced by fixational effort. The power of infrared video-oculography is that it can noninvasively record eye position in total darkness, in darkness with a tiny fixation target present and in light through a semiopaque filter that blocks all fixational input but allows binocular luminance to be modulated."

By comparing the 3-D eye position under these different conditions, the research team aims to quantitatively determine the roles of fixation versus luminance disparity in producing strabismic deviations that arise in children.

IRB approval and plans

Dr. Brodsky received a Mayo Clinic Scholarly Opportunity Award along with approval from the Institutional Review Board (IRB) to use this equipment for clinical diagnosis in children 8 years of age or older, and to use the data collected for future prospective studies. "This equipment will provide new insights into the mechanism of pediatric strabismus and nystagmus," says Dr. Brodsky. Its use may also be applied to the evaluation of surgical and nonsurgical treatments.

Points to remember

Infrared video-oculography is unique in its ability to measure binocular eye position in total darkness.

Because it is noninvasive, video-oculography can be used in children.

This study uses video-oculography to noninvasively determine horizontal, vertical and torsional eye position and provide detailed quantitative information regarding changes in eye position under different stimulus conditions.

Infrared video-oculography is also useful in documenting other neurological forms of nystagmus and determining the efficacy of different forms of treatment.

For more information or to refer a patient to the ocular motor physiology laboratory for eye movement recording, contact Dr. Brodsky at brodsky.michael@mayo.edu or 507-284-2233.

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